Semiconductors, optoelectronics, and other solid state devices have become to be used at higher and higher currents and thereby tend to generate larger quantities of heat. Packaging materials for the encapsulation of these devices require heat resistance and durability at high levels. Among them, packaging materials for optoelectronic devices require satisfactory transparency in addition to the above properties.
To meet the requirements, resin compositions containing an inorganic compound have been being employed as resin materials that excel in properties such as heat resistance, thermal stability (resistance to thermal coloration), and transparency. Patent Literature (PTL) 1 describes cycloaliphatic epoxy resins for the encapsulation of light-emitting diodes and other solid state devices. The epoxy resins contain a boric acid ester and an alkoxysilane. The literature mentions that the resins less deteriorate upon ultraviolet irradiation over a long time. The resins, however, probably have poor resistance to thermal yellowing upon long-term exposure to elevated temperatures of 150° C. or higher, because the resins employ an epoxy resin as a principal component.
Independently, PTL 2 reports polyborosiloxane, an inorganic polymer to form an insulating layer having heat resistance, moisture resistance, and flexibility at high levels, which is obtained by reacting first a bifunctional silane compound with a boron compound to give a product, and further reacting the product with a trifunctional silane compound and a boron compound. The polyborosiloxane, however, has not been examined as an electronic-device packaging material because the polyborosiloxane is solid at room temperature and requires a solvent to form a coating film.